Showing papers in "Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena in 2012"

Recent developments and design challenges in continuous roller micro- and nanoimprinting

Abstract: As an emerging technology for the manufacture of micro- and nano-scale patterns, continuous imprinting; otherwise known as roll-to-roll or roller imprinting, is attracting interest from researchers around the world because of its inherent advantages of low cost, high throughput, large area patterning. This technology is an evolutionary advance on the more traditional nanoimprint lithography developed in the 1990s, which is considered a batch mode, or dis-continuous patterning approach. In recent years, a number of commercial applications have been discovered which require low cost, large area patterning, particularly displays, optical coatings and films, and biological applications such as anti-fouling surfaces and micro-fluidic devices. This review covers a variety of continuous imprinting approaches, highlights challenges, and surveys progress towards high speed production of micro- and nanoscale features for these applications and others using this platform technology.

Monolithic integration of silicon CMOS and GaN transistors in a current mirror circuit

Abstract: GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W...

Combined helium ion beam and nanoimprint lithography attains 4 nm half-pitch dense patterns

Abstract: The authors demonstrated a promising technique that yielded single-digit nanometer features for nanotechnology research and possible future electronic circuit fabrication by combining high resolution helium ion beam patterning and nanoimprint lithography. They fabricated a series of line patterns with single-digit nanometer half-pitches by exposing a layer of hydrogen silsesquioxane (HSQ) resist with a scanning focused helium ion beam. The smallest half-pitch of clearly resolved line patterns was 4 nm. Using the HSQ patterns as a nanoimprint template, nanoscale patterns down to 4 nm half-pitch were transferred into nanoimprint resist through a UV-curable nanoimprint process.

Die singulation technologies for advanced packaging: A critical review

Abstract: Die singulation, also known as wafer dicing, is reviewed in terms of the brief history, critical challenges, characterization of singulation quality, different singulation technologies and underlying mechanisms, and post-singulation die strength enhancement. Mechanical blade dicing has been the workhorse of die separation in the semiconductor manufacturing process. It faces growing challenges due to the adoption of copper/low-k dielectric interconnect structures, thin and ultra-thin wafers, die attach films, narrow dicing streets, and complex stacked structures on the dicing streets. Key dicing quality characteristics are chipping, delamination, kerf geometry, die side wall damage, die surface contamination, and die strength degradation. Various die singulation technologies have been developed to address these challenges and quality issues, including dicing by thinning, laser based approaches, laser and mechanical hybrid method, and plasma dicing. Die strength is a critical parameter for thin and ultra-th...

Electrical conductivity of copper–graphene composite films synthesized by electrochemical deposition with exfoliated graphene platelets

Abstract: Films of graphene/copper composite in copper matrix were deposited on copper foil using an aqueous electrolyte solution of 0.2 M CuSO4 containing graphene oxide suspension at a low current density of 1.75 mA cm−2. Graphene oxide is reduced by further heating the samples in flowing hydrogen atmosphere maintained at 20 Torr and 400 °C for 3 h. The composite samples with different thickness, between 365 and 515 μm, deposited on a Cu foil of thickness 135 μm were characterized for graphene structure, morphology, and distribution. Electrical resistivity and temperature coefficient of electrical resistance of the samples at 300 K were measured using a four-probe method. The results were used to determine the electrical resistivity and temperature coefficient of resistance of the composite layers. The volume fraction and resistivity of graphene were evaluated using effective mean field analysis of the resistivity and temperature coefficient of resistance of the composite films. The results illustrate that the re...

Graphene functionalization and seeding for dielectric deposition and device integration

Abstract: Graphene has recently attracted wide-spread attention because of its unique transport and physical properties that are appealing for a wide range of electronic applications. Integration with scalable high-κ dielectrics is important for the realization of graphene-based top-gated electronic devices, including next generation THz applications. Atomic layer deposition (ALD), a low temperature deposition method based on two separate self-limiting surface reactions, is a preferred technique to achieve high-quality, conformal, ultrathin dielectric films with precise control of thickness and chemical composition at the atomic scale. Unfortunately, ALD of oxides on graphene is hindered by the inertness of the graphene surface. To alleviate this graphene-oxide incompatibility, several different functionalization and seeding methods have recently been developed to render the graphene more susceptible to the ALD process of high-κ dielectrics including: ozone, wet chemical and fluorine pretreatments, low-k polymer se...

Historical development and future trends of vacuum electronics

Abstract: Vacuum electronics (VE) have dominated development and industrial growth in their application areas from the end of the 19th century to the end of 20th century. VE have contributed to basic concepts of physics and have enabled important basic inventions. Despite this bright past, in the meantime also a complete or partial replacement by new technologies such as solid-state electronics (SSE) occurred in several applications areas, triggered by the demand for new features and leading to new applications. Based on a review of the historical development of vacuum electronics from the basic inventions to the modern state of the art, the aim of this paper is to identify future trends and prospects of this field. The appearance of generic technology cycles, as in the case of radio-receiving tubes and cathode-ray display tubes, is discussed. Microwave tubes did experience only a partial replacement by solid-state devices and defended the high-power, high-frequency domain. The reason for their superiority in this domain is discussed. The development of the base technologies for VE, namely vacuum technology and electron source technology, is outlined, enabling further improvements. Besides the high-power, high-frequency domain of microwave tubes, VE technology applications with positive future prospects are addressed, e.g., space applications (long-lived microwave tubes, ion thrusters); thermionic energy converters; e-beam lithography; x-ray tubes; vacuum-based high-resolution characterization, and high-brightness beams for free electron lasers or particle accelerators. The continuous growth and increase in performance of solid-state electronics is shortly reviewed, SSE taking the lead with respect to total sales in the 1980s. Now, despite inherent advantages, solid-state electronics also seem to approach technical limitations. These include increasing energy consumption in conjunction with reduced long-term reliability when further scaling down. It is envisioned that vacuum nanoelectronics can help to overcome these limitations when scaling down feature sizes of integrated circuits below 22 nm.

Characterization of Bi2Te3 and Bi2Se3 topological insulators grown by MBE on (001) GaAs substrates

Abstract: Films of pseudohexagonal Bi2Te3, Bi2Se3 and their alloys were successfully grown by molecular beam epitaxy on GaAs (001) substrates. The growth mechanism and structural properties of these films were investigated by reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction (XRD), high-resolution transmission electron microscopy, and Raman spectroscopy and mapping. The results indicate that the epitaxial films are highly uniform and are of high crystalline quality.

Active layer thickness effects on the structural and electrical properties of p-type Cu2O thin-film transistors

Abstract: The authors investigated the effects of active layer thickness on the structual, optical, and electrical characteristics of p-type Cu2O thin-film transistors (TFTs). It was observed that as the channel thickness increases, the average grain size and root mean square roughness of the Cu2O thin films increase, but the optical transmittance notably decreases, especially in the short wavelength range below 500 nm. The p-type Cu2O TFT device exhibits the cleanest transfer function with only a small subthreshold slope when the channel thickness is 45 nm, whereas notable subthreshold slope humps are observed in the transfer curves for devices with thicker channels.

Graphene metal oxide composite supercapacitor electrodes

Abstract: This study presents composite electrode materials based on graphene oxide (GO) and transition metal oxide nanostructures for supercapacitor applications. Electrophoretic deposition of GO on a conductive substrate was used to form reduced graphene oxide (rGO) films through chemical reduction. The specific capacitance of the rGO was calculated up to 117 F/g at 100 mV/s scan rate from KOH (1 M) electrolyte using an Ag/AgCl reference electrode. The strong interaction of GO with Co3O4 and MnO2 nanostructures was demonstrated in the self-assembled Langmuir–Blodgett monolayer composite, showing the potential to fabricate thin film supercapacitor electrodes without using binder materials. This two-step process is nontoxic and scalable and holds promise for improved energy density from redox capacitance in comparison with the conventional double layer supercapacitors.

In situ near-edge x-ray absorption fine structure spectroscopy investigation of the thermal defunctionalization of graphene oxide

Abstract: In situ near-edge x-ray absorption fine structure (NEXAFS) spectroscopy is used in conjunction with measurements of sheet resistance to examine the electronic structure recovery of graphene oxide upon thermal annealing. Several different defunctionalization regimes are identified with the initial removal of basal plane epoxide and hydroxyl functionalities and subsequent elimination of carboxylic acid moieties. The measured electrical conductivity is closely correlated to recovery of the conjugated π structure. A pronounced broadening of the C K-edge π* resonance is observed upon annealing and is ascribed to the superposition of the NEXAFS signatures of sp2-hybridized domains of varying dimensionality. Such incipient conjugated domains generated upon thermal defunctionalization mediate variable range hopping transport and further lead to an increase in the electrical conductance. Finally, both C K-edge and O K-edge spectra suggest that ring ether functionalities such as pyrans or furans and/or 1,2- and 1,4...

Remote H2/N2 plasma processes for simultaneous preparation of low-k interlayer dielectric and interconnect copper surfaces

Abstract: This study focuses on the simultaneous plasma treatment of interlayer dielectric (ILD) and chemical mechanical polished (CMP) Cu surfaces using N2/H2 plasma processes. The modifications induced by the gas chemistries are investigated for two ILD films with different porosities and carbon concentrations. H atoms and radicals in the plasma react with the carbon groups leading to carbon removal for both of the ILD films. Fourier transfer infrared (FTIR) spectra show a greater fractional reduction of CH3 in the high porosity ILD compared to the low porosity ILD. Results indicate that an N2 plasma forms an amidelike layer on the surface, which apparently leads to reduced carbon abstraction from an H plasma process. In addition, FTIR spectra indicate the formation of hydroxyl (SiOH) groups following the plasma exposure. Increased temperature (380 °C) processing leads to a reduction of the hydroxyl group formation compared to ambient temperature processes, and the dielectric constant is increased by a smaller a...

Optimization of the ammonium sulfide (NH4)2S passivation process on InSb(111)A

Abstract: The passivation of the InSb semiconductor surface and related alloys is of interest due to their small bandgaps and high bulk mobilities, which make them favorable materials for use in quantum-well transistors and long wavelength optoelectronic devices. One of the most common passivation approaches is an ammonium sulfide ((NH4)2S) treatment; however, there are variations in the reported processing conditions for this procedure. This study represents a broad review of the different sulfur treatment parameters used as well as determining the optimal processing parameters in terms of length of time the sample is in the solution and the (NH4)2S concentration, by measuring the level of the residual native oxides, and surface roughness, by means of x-ray photoelectron spectroscopy and atomic force microscopy, respectively.

Low temperature atomic layer deposited Al-doped ZnO thin films and associated semiconducting properties

Abstract: Semiconducting Al-doped ZnO films were deposited by atomic layer deposition at low deposition temperatures of less than 100 °C and used to fabricate transistors. At deposition temperatures of less than 100 °C, the carrier concentrations of the Al:ZnO thin films were below 1018 cm−3, which corresponds to the transparent semiconducting oxide region. The reduced carrier concentrations at low deposition temperatures were attributed to the activation energy for carrier generation of ∼0.7 eV. The devices characteristics of the semiconducting Al:ZnO consisted of mobilities of 1.95 cm2/V s and on–off ratios of over 106. At a positive gate stress of less than 10 V, the Vth shift of the Al:ZnO after 3000 s was ∼3 V, which is almost 1 order of magnitude lower than that of ZnO thin-film transistors.

Large contrast enhancement by sonication assisted cold development process for low dose and ultrahigh resolution patterning on ZEP520A positive tone resist

Abstract: The authors demonstrate a robust, low dose, high contrast, and ultrahigh resolution patterning process based on sonication assisted development of ZEP520A positive tone resist in both room and cold temperature. The contrast as high as γ ∼ 25 and γ ∼ 9.14 can readily be achieved in 6 °C and room temperature development, respectively, in diluted n-amyl acetate solution. The high contrast is demonstrated on 90 nm thick ZEP resist at 20 kV acceleration voltage, from which 20 nm thick titanium lift-off of 60 nm pitch lines and 50 nm pitch dots can be successfully achieved.

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

Abstract: High-quality epitaxial Ge layers for GaAs/Ge/GaAs heterostructures were grown in situ in an arsenic-free environment on (100) off-oriented GaAs substrates using two separate molecular beam epitaxy (MBE) chambers, connected via vacuum transfer chamber. The structural, morphological, and band offset properties of these heterostructures are investigated. Reflection high energy electron diffraction studies exhibited (2 × 2) Ge surface reconstruction after the growth at 450 °C and also revealed a smooth surface for the growth of GaAs on Ge. High-resolution triple crystal x-ray rocking curve demonstrated high-quality Ge epilayer as well as GaAs/Ge/(001)GaAs heterostructures by observing Pendellosung oscillations and that the Ge epilayer is pseudomorphic. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of ∼0.45 nm and room temperature photoluminescence spectroscopy exhibited direct bandgap emission at 1583 nm. Dynamic secondary ion mass spectrometry depth profiles of Ga, As,...

Structural and magnetic characterization of superparamagnetic iron platinum nanoparticle contrast agents for magnetic resonance imaging.

Abstract: The authors report the synthesis, from simple salts, and the physical characterization of superparamagnetic iron platinum nanoparticles (SIPPs) suitable for use as contrast agents in magnetic resonance imaging. The properties of these particles were determined by means of transmission electron microscopy (TEM), thermogravimetric analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), superconducting quantum interference device (SQUID) magnetometry, and nuclear magnetic resonance relaxivity at 4.7 T. TEM showed that the diameters of the particles ranged from 9.3 to 10 nm, depending on the mole ratio of iron to platinum precursors, and on the concentration of octadecylamine (ODA) used in their preparation. The iron to platinum stoichiometry determined by ICP-OES varied from 1.4:1 to 3.7:1 and was similarly dependent on the initial mole ratios of iron and platinum salts, as well as on the concentration of ODA in the reaction. SQUID magnetometry showed that the SIPPs were superparamagnetic and had magnetic moments that increased with increasing iron content from 62 to 72 A·m2/kg Fe. The measured relaxivities of the SIPPs at 4.7 T were higher than commercially available superparamagnetic iron oxide nanoparticles, suggesting that these particles may be superior contrast agents in T2-weighted magnetic resonance imaging.

Comparison of tunnel junctions for cascaded InAs/GaSb superlattice light emitting diodes

Abstract: Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. In this study, a variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. Here we used GaSb on the p-side of the junction, while varying materials on the n-side. The authors find Al0.20In0.80As0.73Sb0.27 tunnel junctions function best due to the low set of the conduction band; Ga0.75In0.25As0.23Sb0.77 also works well, though is more resistive due to a reduced set of the conduction band; and GaSb, while giving good hole confinement, results in a very resistive junction. Graded superlattice junctions can also work well, though they show sensitivity to doping levels, and present some challenges in growing strain-free.

Boron filling of high aspect ratio holes by chemical vapor deposition for solid-state neutron detector applications

Abstract: A multiple deposition and etching process has been developed to enable high fill factor boron deposition in high aspect ratio holes fabricated in a (100) silicon substrate. The boron deposition was carried out using low-pressure chemical vapor deposition and the etching was done by inductively coupled plasma reactive ion etching technique. The boron deposition processes were carried out under different conditions in order to find a baseline process condition. The boron etching processes done under different conditions with the photoresist as the mask are also discussed. Finally, the fabricated neutron detector with the highest fill factor was characterized for the thermal neutron detection efficiency.

Fabrication of 5 Tdot/in.2 bit patterned media with servo pattern using directed self-assembly

Abstract: The fabrication of an etching template for 5 Td/in.2 bit patterned media using a self-organization material, namely, poly(styrene)-poly(dimethylsiloxane) (PS-PDMS), was investigated. The molecular weight of the PS-PDMS for forming the areal density of 5 Td/in.2 dot pattern was estimated from the polymerization index related to the Flory–Huggins interaction parameter. Annealing was carried out to obtain a fine-order dot pattern. PS-PDMS films were subjected to thermal treatment or solvent annealing. The ordering of the dot array in these films was evaluated by using Voronoi diagrams. The results indicate that the film annealed in N-methylpyrrolidone (NMP) vapor showed finer ordering than did the thermally treated film. This seemed to be attributable to the high solubility parameter of NMP. The soaking of NMP into the PS phase slightly shifted the phase separation energy of the polymer matrix. The lattice spacing of the obtained hexagonal pattern was 11 nm. By using low-molecular-weight PS-PDMS with solvent...

Behavioral model for electrical response and strain sensitivity of nanotube-based nanocomposite materials

Abstract: An algorithm to study the electrical conductivity of nanocomposite layers, made by dispersing nanotubes inside a polymer structure, is proposed. Conduction is modeled by following the path of electric current through the nanotube network within the polymer. Based on this algorithm, a numerical simulator is developed to study the effect of nanoparticles and nanocomposite film dimensions and concentration on the conductance of a nanocomposite resistor. This simulator is also capable of predicting the behavior of nanocomposite resistors under mechanical strain for devices with different parameters. To verify the simulation results, several test devices with different filler concentrations are fabricated from a composite of SU-8 and multiwall carbon nanotubes. The experimental results agree with the performance anticipated by the simulator, as the applied strain and filler concentration are altered independently. The simulator is capable of illustrating the tradeoffs between conductivity, sensitivity, and rep...

Visualization of beams from ionic liquid ion sources for focused ion beam applications

Abstract: Ionic liquid ion sources (ILIS) share qualities with liquid metal ion sources necessary for focused ion beams (FIB) operation, such as pure ion emission and low energy spreads. These sources work at lower currents, room temperature, and are able to produce both positive and negative ions from a large number of ionic liquids. The influence of the applied voltage on the beam emitted from the ILIS based on the liquid EMI-BF4 (1-ethyl 3-methyl imidazolium tetrafluoroborate) is characterized by using a beam visualization system. As the applied voltage is increased, the source transitions from single to multiple beam emission. The visualization tool is also used to determine the spatial distribution of the neutral particle population contained within the beam emitted from ILIS. Cluster ions can break during flight, yielding a new ion and neutral particles. This neutral population can be highly energetic, and might be of interest for material treatment applications where charging of targets is undesirable. For F...

Homoepitaxial N-polar GaN layers and HEMT structures grown by rf-plasma assisted molecular beam epitaxy

Abstract: The authors have investigated the growth and structural and electrical properties of homoepitaxial GaN layers and GaN/AlGaN heterostructures grown on free-standing, hydride vapor phase epitaxy grown, N-polar GaN:Fe substrates by rf-plasma molecular beam epitaxy. Secondary-ion mass spectroscopic analysis of unintentionally doped and Be-doped N-polar GaN layers indicate that oxygen is the dominant impurity in all layers and is largely insensitive to growth temperature in the range investigated (675 °C < TS < 760 °C). Transmission electron microscopy (TEM) indicates that threading dislocations are generated at the regrowth interface in these samples; in contrast to homoepitaxial growth on Ga-polar GaN, and that the density of threading dislocations diminishes as the growth temperature increases. However, examination by TEM indicates that threading dislocations are not generated at the regrowth interface of samples subjected to pregrowth substrate surface cleaning by gallium deposition and desorption and subsequent growth of ultrathin (15 A) initial AlN layers. N-polar GaN/AlGaN heterostructures grown on Be-doped homoepitaxial N-polar GaN buffers exhibit low buffer leakage and Hall mobilities up to 1680 cm2/Vs at sheet densities of 1.3 × 1013 cm−2. High electron mobility transistors have been fabricated on these structures; drain current densities over 700 mA/mm and breakdown voltages as high as 70 V have been measured.The authors have investigated the growth and structural and electrical properties of homoepitaxial GaN layers and GaN/AlGaN heterostructures grown on free-standing, hydride vapor phase epitaxy grown, N-polar GaN:Fe substrates by rf-plasma molecular beam epitaxy. Secondary-ion mass spectroscopic analysis of unintentionally doped and Be-doped N-polar GaN layers indicate that oxygen is the dominant impurity in all layers and is largely insensitive to growth temperature in the range investigated (675 °C < TS < 760 °C). Transmission electron microscopy (TEM) indicates that threading dislocations are generated at the regrowth interface in these samples; in contrast to homoepitaxial growth on Ga-polar GaN, and that the density of threading dislocations diminishes as the growth temperature increases. However, examination by TEM indicates that threading dislocations are not generated at the regrowth interface of samples subjected to pregrowth substrate surface cleaning by gallium deposition and desorption and subs...

Integrated processing of contrast pulse sequencing ultrasound imaging for enhanced active contrast of hollow gas filled silica nanoshells and microshells.

Abstract: In recent years, there have been increasing developments in the field of contrast-enhanced ultrasound both in the creation of new contrast agents and in imaging modalities These contrast agents have been employed to study tumor vasculature in order to improve cancer detection and diagnosis An in vivo study is presented of ultrasound imaging of gas filled hollow silica microshells and nanoshells which have been delivered intraperitoneally to an IGROV-1 tumor bearing mouse In contrast to microbubbles, this formulation of microshells provided strong ultrasound imaging signals by shell disruption and release of gas Imaging of the microshells in an animal model was facilitated by novel image processing Although the particle signal could be identified by eye under live imaging, high background obfuscated the particle signal in still images and near the borders of the tumor with live images Image processing techniques were developed that employed the transient nature of the particle signal to selectively filter out the background signal By applying image registration, high-pass, median, threshold, and motion filtering, a short video clip of the particle signal was compressed into a single image, thereby resolving the silica shells within the tumor © 2012 American Vacuum Society

Inductively coupled plasma deep etching of InP/InGaAsP in Cl2/CH4/H2 based chemistries with the electrode at 20 °C

Abstract: A Cl2/CH4/H2 inductively coupled plasma process without additional heating or wafer bonding is developed for the InP/InGaAsP material system. Vertical and smooth sidewalls can be observed in the scanning electron microscope images. The main factors of etch rate, selectivity, and sidewall roughness are analyzed relative to the gas concentration in a full factorial design of the experimental procedure. Under optimized conditions, an etch depth of more than 3 μm with smooth and vertical sidewalls can be obtained. A strong indication of a passivation effect of CH4 is obtained.

Studies on InAs/GaSb superlattice structural properties by high resolution x-ray diffraction

Abstract: This paper presents work on InAs/GaSb superlattice structural property studies. The superlattice materials were grown by molecular beam epitaxy and measured by high resolution x-ray diffraction, and measured x-ray rocking curves were fitted to the simulated ones in order to fully analyze the superlattice structures. A four-layer model including an InAs layer, a GaSb layer and two interface layers was used for simulation. The results show that the two interface layers are ternary compounds of InSbAs, which have, respectively, an Sb composition of 0.99 at the InAs-on-GaSb interfaces and an Sb composition of 0.01 at the GaSb-on-InAs interfaces. This is the first article, to our knowledge, on the detailed analysis of the InAs/GaSb superlattice interface structures. The experiments also demonstrate that the As flux during the epitaxy growth affects the interface layer InSbAs compositions and hence the lattice mismatch between the superlattices and the substrates. With an As beam equivalent pressure change from...

Structural properties of InAs/InAs1–xSbx type-II superlattices grown by molecular beam epitaxy

Abstract: Strain-balanced InAs/InAs1−xSbx type-II superlattices (SLs) have been proposed for possible long-wavelength infrared applications. This paper reports a detailed structural characterization study of InAs/InAs1−xSbx SLs with varied Sb composition grown on GaSb (001) substrates by modulated and conventional molecular beam epitaxy (MBE). X-ray diffraction was used to determine the SL periods and the average composition of the InAs1−xSbx alloy layers. Cross-section transmission electron micrographs revealed the separate In(As)Sb/InAs(Sb) ordered-alloy layers within individual InAs1−xSbx layers for SLs grown by modulated MBE. For the SLs grown by conventional MBE, examination by high-resolution electron microscopy revealed that interfaces for InAs1−xSbx deposited on InAs were more abrupt, relative to InAs deposited on InAs1−xSbx: this feature was attributed to Sb surfactant segregation occurring during the SL growth. Overall, these results establish that strain-balanced SL structures with excellent crystallinit...

Extraction of a low-current discharge from a microplasma for nanoscale patterning applications at atmospheric pressure

Abstract: The authors present a scheme to extract a low-current discharge from a microplasma at atmospheric pressure for nanopatterning applications. The extracted discharge is generated by applying a high positive voltage to an independent electrode and accelerating electrons from the microplasma. Current-voltage (I–V) characteristics of the extracted discharge show high stability at low currents and tunability over a wide range of currents. Exposure of metal precursor loaded films to the extracted discharge results in electrochemical reduction of metal ions to solid metal, as confirmed by X-ray photoelectron spectroscopy. Combining this approach with masking techniques allows the transfer of nanoscale patterns of metal at ambient conditions.

Bilayer graphene by bonding CVD graphene to epitaxial graphene

Abstract: A novel method for creating bilayer graphene is described where single-layer CVD graphene grown on Cu is bonded to single-layer epitaxial graphene grown on Si-face SiC. Raman microscopy and x ray photoelectron spectroscopy demonstrate the uniqueness of this bilayer, as compared to a naturally formed bilayer, in that a Bernal stack is not formed with each layer being strained differently yet being closely coupled. Electrical characterization of Hall devices fabricated on the unusual bilayer show higher mobilities, and lower carrier concentrations, than the individual CVD graphene or epitaxial graphene layers.

Impact of ultrathin Al2O3 interlayer on thermal stability and leakage current properties of TiO2/Al2O3 stacking dielectrics

Abstract: Ultrathin TiO2/Al2O3 stacking structures were fabricated using an atomic layer deposition technique. The effect of the ultrathin Al2O3 interlayer on interfacial thermal stability and leakage current properties were studied. After thermal annealing of the TiO2/Al2O3/TiO2/Al2O3/Si structure at 700 °C for 60 s, the Al2O3 double layers remained amorphous, although the layers of TiO2 were crystallized. The amorphous Al2O3 divided the grain boundaries which would otherwise serve as diffusion paths for atoms and as leakage current channels from the TiO2 layers. As a result, atomic diffusion and surface roughness were suppressed, and the leakage current value was reduced by about a 1.5 order of magnitude compared with TiO2/Al2O3/Si. The improved interfacial stability as well as the reduced leakage current density indicates the present stacking structure has potential application in future high-performance microelectronics.